Studies on the development of the fetal lung have shown that this organ is particularly responsive to the hormone hydrocortisone. However, the specific cellular response to hydrocortisone given by cells comprising the lung is difficult to ascertain in vivo because of interactions with heterologous cell types and the synergistic and/or modulating influences of other hormones. One can minimize the above interactions by studying the response to hydrocortisone by lung derived cells in tissue culture. Previous studies on the effect of hydrocortisone on human fetal lung cells in culture have shown an increased rate of cell division, a longer in vitro life span and a response that is specific for hydrocortisone. One of the first biochemical changes to occur following interaction of a hormone with its target tissue are changes in histone acetylation and modulation of the chromatin template activity of the tissue. It is the purpose of this study to determine if changes in the rate of histone acetylation and chromatin template activity are associated with the interaction of hydrocortisone and human fetal lung cells in tissue culture. Any association of the hormone with chromatin prior to eliciting a biochemical response will also be determined.